1. Field of the Invention
The present invention relates to a structure and method of forming a buffering layer, and more particularly to a structure and method of forming a metal buffering layer in a manufacture process of a conductive bump.
2. Description of the Prior Art
Conventionally, the I/O bonding pads are distributed on the surroundings of chips of a wafer, as the original design concerned or for easily printing wires. In order to redistribute the distribution of the I/O bonding pads, a rerouting (or redistribution) technology of the manufacture process of a conductive bump is used for changing the surrounding arrangement into the dispersing arrangement of the bonding pads to achieve the demand of miniaturizing a package size. Referring to FIG. 1, a wafer 110, thereon, has at least a bonding pad 120 and a passivation layer 130 exposing a portion of the bonding pad 120. A dielectric layer 140 covers the passivation layer 130 and exposes the exposed portion of the bonding pad 120, and can be made of a certain material, such as Benzocyclobutene (BCB). Subsequently, forming a metal layer as a redistribution layer (RDL) on the dielectric layer 140, then, etching the redistribution layer to form a demanded circuit trace 150. Another dielectric layer 160 is formed on the exterior layer and a portion of the circuit trace 150 is exposed. Finally, an under bump metallurgy layer (not shown) and the conductive bump 170 are formed in turn on the exposed portion of the circuit trace 150 to change the distribution of the I/Os.
The above-mentioned packaging structure often incurs a collapsing problem of the circuit trace 150, and that reduces the reliability of the packaged wafer. In addition, due to the circuit trace 150 being bulged on the dielectric layer 140, the surface covered by the dielectric layer 160 is not perfectly flat, and furthermore the flatness of the exterior surface of the dielectric layer 160 is also influenced. Therefore, it is necessary to provide a new method and structure to overcome the disadvantages of the conventional packaging structure and increase the reliability of the packaged wafer.